This application is a continuation of pending international application PCT/EP01/03379 filed Mar. 24, 2001 and which designates the U.S.
The invention relates to a bottom element for a device for treating particulate material, having a two-dimensional bottom, in which are provided numerous apertures, via which a treatment medium can be passed through the bottom, and having means that impose a motion component in the direction of the plane of the bottom on the treatment medium flowing through the bottom.
A device with a bottom element of this kind is known from EP 0 370 167 A1.
The device described in this document is used to dry, granulate or coat a particulate material.
In this case, a gaseous medium, referred to as process air, is, for example, introduced into a process chamber via the bottom, passing approximately horizontally and in the circumferential direction into the process chamber through the numerous apertures in the bottom.
In this device, the bottom comprises a ring of baffle plates, which extend radially and overlap one another circumferentially. Via the apertures formed in the overlapping region between the overlapping baffle plates, the treatment medium passes through the bottom and into the process chamber. The mutually overlapping baffle plates are set approximately horizontally or slightly obliquely and, as a result, impose a motion component in the direction of the plane of the bottom on the treatment medium flowing between the overlapping plates. Depending on the alignment of these baffle plates, the process air enters the process chamber more or less horizontally and in a circumferential direction. Owing to the initially horizontally directed component of the process air, the particulate material to be treated flows in the form of a rotating band of material on a kind of cushion of process air. Nozzles can be arranged in the bottom, between the baffle plates, in order to spray a liquid treatment medium on the particulate material to be treated.
The disadvantage with a bottom element of this kind constructed from overlapping baffle plates is that it is very expensive to manufacture. First of all, the approximately trapezoidal individual plates must be produced and assembled in the overlapping arrangement to give a ring.
The number of apertures for the passage of the treatment medium is thus determined by the number of plates. In the case of bottom elements with large diameters, there is the problem that the trapezoidal plates are very wide in the circumferential direction in the radially outer region. Since the treatment air or process air emerging from the apertures between the plates must accelerate the particles of material treated in the process chamber, a particle of material moving at a position disposed very radially outward is moved again in front of an aperture from which process air is emerging only after traveling a relatively long distance. A particle which is moving circumferentially more radially inwards, on the other hand, meets an aperture again after a much shorter distance of travel. Precautions therefore have to be taken to compensate for this. This was carried out in such a way, for example, that the height of the aperture between two overlapping baffle plates was made larger in the radially outward direction, e.g. by raising the overlapping baffle plate obliquely as seen in the radially outward direction. This then enabled more process air to emerge in radially outer regions in order to achieve acceleration motion components in the region of two successive apertures that were as similar as possible.
However, this had the effect that, in the case of bottom elements of large diameter, the radially outer plates are raised, thus presenting mechanical resistance surfaces to the material to be treated. Since such devices are used especially in the pharmaceutical sector, there was therefore the risk, when coating tablets for example, that there would be spalling on the tablets owing to collisions with these raised radially outer regions of the baffle plates. The distribution of the treatment medium, whether a gaseous or liquid medium or one containing solids, or a mixture of these, is thus not optimal. The relatively large apertures between the plates entail the risk that the material will fall through the bottom.
It is therefore the object of the present invention to provide a remedy here and to provide a bottom element of the type stated at the preamble which can be produced in a simple manner in terms of manufacturing technology and allows optimum guidance of the treatment medium.
According to the invention, the object is achieved by virtue of the fact that the bottom is designed as a plate-shaped body, said apertures are designed as slots, said slots have been generated by a removal of material from said plate-shaped body, and wherein said slots have side walls sloping towards the plane of the bottom, thereby imposing to the treatment medium said motion component when passing said slots. For facilitating a cleaning of said bottom, said side walls further consecutively taper to a side of the bottom the particulate material rests.
In terms of manufacturing technology, these measures have the advantage that it is now no longer necessary to produce individual baffle-plate elements, which then have to be assembled in an involved process to form a bottom, but that only a two-dimensional bottom has to be provided, from the material of which the numerous slots are then formed by removal of material. This makes it possible to select the number, shape, length, width, angle of inclination and pattern of the slots as a function of the treatment process and of the product to be treated. The motion component in the direction of the plane of the bottom is produced by virtue of the fact that the aperture cross sections of the slots slope in an appropriate manner.
This now allows significantly greater variation as regards the guidance of the process air. Thus, it is possible, for example, for a large number of relatively narrow slots to be provided, through which the process air can then be uniformly distributed and motion component aligned at the appropriate angle of inclination or in the direction of the plane of the bottom. The numerous relatively narrow slots prevent the material from falling through the bottom down to a size of material corresponding to the width of the slots. In the case of a circular or annular bottom, an appropriate number of slots can then be made in the radially outer regions in order thereby to compensate for the longer circumferential path in radially outer regions.
In terms of manufacturing technology, such removal of material can be carried out rapidly, easily and with high precision, e.g. by laser cutting, water-jet cutting, by combinations of these methods, by erosive methods or even by milling.
This simple structure also allows the possibility of providing different bottom elements for one apparatus, allowing optimum treatment of the particulate material depending on its size, whether it is, for example, fine powder or oblong tablets in the centimeter range. Rapid exchange of the bottom element is easily possible by virtue of the simplicity of the design.
The necessary cleaning too, which must meet high standards especially in pharmaceutical technology, is made considerably easier since there is not a large number of individual parts assembled to form an overlapping ring but a single plate-shaped body, in which corresponding slots have been made.
Due to the consecutively tapering of the side walls of the slots in a direction to that side of the bottom, the particulate material rests, no particles can enter into a slot and obstruct it.
If a particle having a size smaller than the width of the slot enters the slot at the side the particles are present, this particle will fall through the slot downwards but does not obstruct it, since in the downwards direction the side walls diverge.
In a further embodiment of the invention, the slots run in a straight line.
Slots of this kind are particularly simple to make in terms of manufacturing technology, and the straight-line geometry of the slots allows regular slot patterns, in particular slot patterns aligned in parallel.
In further embodiments, the slots are curved.
This measure has the advantage that longer slots can be made on a surface element through the curvature than with just a straight-line slot, making this measure particularly advantageous when as large as possible an exit area for certain predetermined parameters, e.g. slot width, is to be achieved per surface element.
In a further embodiment of the invention, the slots extend toward a central center of the bottom.
This alignment then allows guidance of the air in a circle on the bottom, possibly with the formation of a toroidally rotating band, a geometry which has proven particularly favorable for the treatment of particulate material.
In a further embodiment of the invention, in the case of a circular bottom, the slots extend radially.
This slot pattern is particularly favorable to the formation mentioned above of a circular, toroidally rotating band of material.
In a further embodiment, the further the slots are from the center, the more of them there are in the circumferential direction.
This measure has the advantage that the provision of an increasing number of slots compensates for the differences in distance traveled between particles of material circulating more radially inwards and particles of material circulating more radially outwards. In other words, a particle of material circulating radially outwards crosses a slot approximately after the same distance as a particle circulating radially inwards, and the particles can thus be accelerated uniformly. This leads to uniform treatment of the material, irrespective of whether a particle of material is being moved radially further toward the inside or radially further toward the outside.
In a further embodiment, there is a row of slots lying close together in the outer circumferential region.
This measure has the advantage that the critical transitional zone between the outer circumferential edge of the bottom and the housing accommodating the latter is virtually blown free by virtue of the large number of slots, excluding the possibility that material will gradually accumulate in this angular zone.
In a further embodiment of the invention, there are openings in the bottom to accommodate spray nozzles.
This measure then allows additional treatment of the material with a liquid sprayed medium, directly in the region of the bottom, when coating for example.
In a further embodiment of the invention, there are slots in the bottom that at least partially surround the openings in the region of these openings.
This measure has the advantage that optimum flow conditions around the nozzles can be created in a specifically intended manner by the provision of slots in the area surrounding these openings for the nozzles, thus preventing the accumulation of material in the reduced-pressure region surrounding the nozzles, the surrounding area thus being kept free by the provision of these additional slots. This is in fact possible because these additional slots can be made very easily in terms of manufacturing technology.
In a further embodiment of the invention, the bottom is flat.
This measure has the advantage that there is a particularly homogeneous surface without mechanical obstructions for the product.
In a further embodiment of the invention, the bottom is contoured.
This measure is advantageous if undulating movements are desired, or unwanted undulating movements can be compensated for by appropriately contoured bottoms.
In a further embodiment of the invention, the bottom is rotatable.
This measure has the advantage that the rotary motion provides an additional variation parameter for moving the material. Rotation of such a simple component as the bottom element is considerably easier to accomplish than assembly of different baffle plates.
In a further embodiment of the invention, a longitudinal center line of the aperture cross section is at an acute angle to the plane of the bottom, preferably in the region of 5xc2x0 to 85xc2x0, most preferably in a range of 30xc2x0 to 60xc2x0.
In these annular ranges, optimum treatment results can be achieved for a large range of material to be treated.
In a further embodiment of the invention, a plurality of slots, which are separated from one another by bridges of material, are arranged in series as seen in the direction of extension of the slots.
This measure has the advantage that, although a multiplicity of slots can be provided, the bottom still has adequate mechanical stability thanks to the bridges of material between the slots.
In a further embodiment of the invention, the bottom is annular and a cone is provided centrally on the side of the outflowing treatment medium.
This assembly allows the formation of the toroidally rotating band on an annular bottom in a particularly favorable manner. This compact construction element can also be used, for example, to convert existing systems operating on this principle.
It is self-evident that the features mentioned above and those that will be explained below can be used not only in the combination indicated but also in other combinations or alone without exceeding the scope of the present invention.